And how to understand what sport generates more interested clients now? Where can I find this statistics?
I don't think you need that statistics, because your incomes will probably depend on your money and coefficients that you have, not from the number of clients and their bets in certain kind of sport. It means you can earn much in every sport you'll choose.
Especially if you use bid strategies...
Usually every professional gambler has a well-developed plan that helps increase the chance that the bet will play